The present disclosure relates to a tandem type image forming apparatus such as a color multifunction device.
Tandem image forming apparatuses, such as an intermediate transfer type color multifunction device, have an intermediate transfer belt looped over a driving roller and a driven roller, and a plurality of photosensitive drums for yellow, cyan, magenta, and black positioned along the surface of the intermediate transfer belt. The tandem image forming apparatuses also have a charger, a developing device, a drum cleaning device, and others for each photosensitive drum. The peripheral surfaces of the photosensitive drums are charged by the chargers and are exposed by exposure devices, and electrostatic latent images are thereby formed. Toner is attached to these electrostatic latent images by developing devices, and toner images are thereby formed. The toner images formed on the peripheral surfaces of the photosensitive drums are transferred (primarily transferred) to the surface of the intermediate transfer belt so as to be superposed on each other. Next, the toner images multiply transferred to the intermediate transfer belt are transferred (secondarily transferred) to a sheet, and a color image is thereby formed on the sheet. Toner remaining on the peripheral surfaces of the photosensitive drums after the primary transfer is removed by the drum cleaning devices.
Many of the above-described image forming apparatuses have a neutralization device for each photosensitive drum. The neutralization device removes surface potential, such as an electrostatic latent image, remaining on the peripheral surface of the photosensitive drum after a toner image is primarily transferred to the intermediate transfer belt. The neutralization device irradiates a predetermined area on the peripheral surface of the photosensitive drum from a primary transfer position to a charging position where the photosensitive drum is charged by the charger, with neutralization light from a neutralization light source, and performs neutralization (post-transfer neutralization) of the surface potential of the photosensitive drum.
However, if the surface potential remaining on the peripheral surface of the photosensitive drum cannot be sufficiently removed by the post-transfer neutralization, unevenness of surface potential remains on the peripheral surface of the photosensitive drum even after the peripheral surface of the photosensitive drum is charged by the charger. This can result in so-called image memory. For example, after a dark image is formed, a large amount of toner is not primarily transferred and remains, neutralization light is blocked and sufficient neutralization is not performed, and therefore image memory occurs.
It is effective in suppressing the occurrence of image memory to perform, before the primary transfer, neutralization (pre-transfer neutralization) by irradiating the surface of the photosensitive drum after developing with neutralization light, and to thereby facilitate the transfer of the toner image on the photosensitive drum to the intermediate transfer belt.
In order to perform pre-transfer neutralization, in addition to post-transfer neutralization, and to thereby suppress the occurrence of image memory, in addition to a device that emits neutralization light for post-transfer neutralization, a device that emits neutralization light for pre-transfer neutralization in the image forming apparatus may be provided.
In the case of a tandem image forming apparatus, a neutralization device for post-transfer neutralization and a neutralization device for pre-transfer neutralization may be provided for each of the four photosensitive drums. However, it is difficult to find space for these neutralization devices without increasing the size of the apparatus. In addition, the electric wiring to these neutralization devices is complicated, and the manufacturing cost of the image forming apparatus therefore increases.